Part of my contribution to the WSJ's coverage of the 2017 GOP federal tax overhaul legislation.

Two percentage points are generating a big tussle in the debate over the right corporate tax rate.

As House and Senate lawmakers continue hashing out differences between their tax-overhaul bills, the prospect lingers that they could push the new corporate tax rate to 22%.

Both chambers passed bills that would have cut it to 20%, down from 35% today, as part of a broader package of tax-law changes, and lawmakers are eager to keep it there. Still, President Donald Trump has raised the possibility of such a change, and pressure is growing in some quarters to find money for a variety of interests, from lower-income workers to small grocers.

A 22% corporate rate instead of a 20% one is significant, amounting to about $200 billion in tax revenue over 10 years, based on a rule of thumb that puts each percentage point of corporate tax at about $100 billion over that period, tax experts say.

For U.S.-based companies, either cut would be sharply lower than today’s 35% statutory corporate rate, and push the U.S. rate below that of most major developed countries. “In the end, Corporate America will write a lovely thank-you note to the Congress of the United States, regardless which of those tax rates ends up being imposed,” said University of Southern California law professor Edward Kleinbard.

Moody’s Corp., the bond-rating giant, offered a glimpse of that contrast in a presentation to investors and analysts last week. The company’s effective tax rate under current law is about 30%, Chief Financial Officer Linda Huber said. Each percentage-point reduction in that figure would increase earnings by 7 cents to 8 cents a share.

So cutting the firm’s effective tax rate to 20% would raise earnings by 70 to 80 cents a share, Ms. Huber said, or between $134 million and $153 million using the company’s Sept. 30 share count. She suggested the difference between that and a 22% rate would mean giving up between 14 cents and 16 cents of that benefit. In 2016, Moody’s reported earnings of $1.36 a share, or about $267 million.

Lawmakers are seeking to give companies a reason to invest in the U.S. rather than overseas, and they worry that effort will fail if they adopt a tax rate that isn’t low enough—particularly because other countries are likely to cut their rates in response.

“That’s the whole idea, is to come in at below the average,” Sen. Rob Portman (R-Ohio) told reporters last week. “If we go ahead and take it up to the average or above, then we’re not giving our workers the competitive advantage we’re trying to provide here.”

Companies might be more amenable to a slightly higher rate if that means lawmakers ditch other tax-overhaul provisions they don’t like.

That could include a Senate proposal to maintain the corporate alternative minimum tax, or AMT, or provisions that postpone some tax cuts—the Senate bill puts off the corporate cut until 2019—and make others temporary.

Delays encourage gaming the tax system, as companies consider putting off or accelerating spending to maximum effect, while temporary provisions complicate corporate-tax planning, said Steven Rosenthal, senior fellow at the Tax Policy Center, a nonpartisan think tank run by a former Obama administration official.

“Whatever changes we want to make to the corporate tax rate, we should make it immediate and make it permanent and pay the price,” Mr. Rosenthal said.